1. Technical Field
The present invention relates to the packaging of food products and specifically it relates to the packaging of cooked food products that must be cooled before packaging is completed. Even more specifically, the invention relates to packaging of porous, snack foods that are packaged in rigid containers.
2. Description of Related Art
A variety of packaging techniques have been used to package prepared food products. These can loosely be grouped into flexible, semi-rigid, or rigid packages. With products such as formed potato chips, which have a regular shape for stacking, rigid or semi-rigid containers can be used.
In an exemplary situation, a product, such as a formed potato chip is produced and packaged in a process shown in FIG. 1A. During the process, the chips will travel down a production line, the layout of which is shown in FIG. 1B, where the layout of the line closely parallels the process. In this process, the product is first prepared for cooking (step 110) at the dough preparation area 115. Generally, potato flakes are mixed with water and other ingredients to make a potato dough. The dough is preferably chilled to make handling easier, then rolled out on a sheeter to form a flat sheet of dough, and cut into individual chips. The chips are then cooked as by baking or frying (step 120) in an oven or fryer 125 to a predetermined color and dryness, depending on the desired product. Once the chips have been cooked, an optional seasoning may be applied (step 130) to the top of the chips at seasoning station 135. This seasoning step must take place prior to the time the temperature of the chips falls below about 150° F. or the seasoning will not stick to the chips. The chips are cooled (step 140) at cooling station 145 by forcing cold air over the chips as they move through this step. FIGS. 2A and 2B illustrate the chips 206 moving along a conveyor belt 204 at the cooling station 145, with cooling air being blown down on them from air manifold 202. It has been generally considered that the most efficient method of cooling the chips would be to present them in a single layer as they pass under the manifold, although this takes up a large amount of linear space to allow the chips to be spread out in this fashion while cooling. A compromise situation is shown in FIG. 2A, where the chips 206 are overlapped to present a portion of their surface to the cooling air but not take up as much room in the line. As shown in FIG. 2B, several rows of chips 206 can move side-by-side through the cooling station 145. The air used for cooling must be blown at a low velocity to ensure that the seasoning is not blown away or the chips misaligned by the airflow. Thus the rate of heat transfer and the subsequent cooling of the chips is limited by the available air velocity. When the chips have reached an acceptable temperature, they are stacked and loaded into a canister (step 150) at the canister loader 155. A seal is first applied (step 160) to the top of the canister at the sealer 165 to ensure freshness and prevent tampering, then the canister is capped (step 170) at the capper 175 with a reusable cap for consumer use. The canisters are labeled (step 180) at the labeler 185 and packaged in cases (step 190) at the case packing station 195 for distribution to the consumer. Depending on the specific product, these can be shipped to various locations worldwide.
One problem encountered when the product is packaged in a rigid package is the inability of a rigid package to change shape with changes of the environment, such as temperature and pressure. When the product is packaged while still hot, a large pressure differential can develop between the inside and the outside of a sealed, rigid package, particularly if the package is subsequently stored at a lower altitude or a colder temperature.
The assignee of this application has designed a rigid canister made of a composite material in which to package formed chip products, such as the formed potato chips discussed above. The canister has been designed with an inherent strength to resist an internal vacuum that is created at packaging, but if the conditions under which the product is stored differ too much from the conditions under which it was packaged, the vacuum within the package can cause the package to implode.
The temperature at which the product is packaged is a key variable in the creation and extent of the vacuum within the canister. There is typically a large amount of airspace in a canister of formed chips, due to the space between each pair of chips, the inherent porosity of the chips, and the space between the chips and the sidewalls and top of the canister. The contained gas will shrink significantly in volume with cooling temperatures. It should be noted in passing that the formation of a strong vacuum is not an issue with liquids in a rigid container, since they generally have only a small airspace. To avoid the relatively large vacuum that can be generated when food products such as stacked potato chips are sealed in a rigid container, the current practice in the industry is to cool the product prior to packaging, as shown in the method of FIG. 1A. It has been an axiom of engineering that more efficient cooling will be achieved if the product is cooled in a mono-layer bed with forced air, but as mentioned above, this concept imposes problems of its own, namely 1) the provision of space to cool the product, 2) the integration of seasoning with cooling, 3) the prevention of oil strippage, and, when products are stacked, 4) the prevention of movement of the product during cooling. Each of these problems will be discussed.
1) For a facility in which food products are cooked and packaged, the space required to keep the product in a mono-layer for cooling can add to the cost of both machinery and floor space. In an exemplary situation, a stack of chips spread out in a horizontal, mono-layer fashion for cooling can add on the order of 27 inches of horizontal space to the line for each canister of chips. Adding this much space to multiple lines that package a given product can be a significant expense just for cooling.
2) Many products are seasoned after cooking. As seen in FIG. 1A, seasoning is generally done prior to cooling the chips in order to enhance the seasoning adhesion to the product. However, once the chips are seasoned, the use of high velocity air can cause much of the seasoning to be blown off the chip, which of course affects taste and/or cost. To avoid this, the velocity of air must be reduced, further increasing the time, and therefore distance, that must be allocated for cooling. This, again, adds to the cost.
3) For non-seasoned chips, blowing high velocity air onto the chip can strip its surface oil. Lowering the level of oil in the finished product can adversely affect the taste and consumer acceptability, so air velocity must remain low even for unseasoned chips.
4) Because the product to be packaged in the rigid container is first stacked, the use of high velocity air can blow the chips out of position, affecting the stacking mechanism. Like items 2) and 3) above, the solution to this problem requires lower velocities of air and longer distances for cooling.
Thus, the current technology of cooling for stacked chips has a high capital expense. It would be desirable to find another method of cooling a stackable food product that did not have these drawbacks.